Based on Mick Jagger's serious expression and Keith Richards' focused stare, it was clear the pressure was on.

It was the summer of 1972, and the Rolling Stones were on their American concert tour for their acclaimed "Exile on Main Street" album. But when they were not onstage and rocking out with their fans, they were hard at work remixing tracks at the Sunset Sound studio in Hollywood.

It was a heady time filled with parties and recording sessions and only one person was there to capture it all intimately -- famed music photographer Jim Marshall, who was covering the tour for Life magazine.

Now the estate of Marshall is releasing some of the never-before-seen photos of the band in a new book "The Rolling Stones 1972" (Chronicle Books), out on August 15. There will also be a show at New York's Steven Kasher Gallery from July 5 to September 8, and an exhibit at EMP Museum in Seattle, opening on July 14. Some of these frames are being displayed exclusively on the CNN Photos blog. The release couldn't have had better timing as the Rolling Stones recently announced plans to mark their 50th anniversary this year.

Amelia Davis, a photographer who worked as Marshall's assistant, is the sole owner of Jim Marshall Photography. (Marshall died in 2010.) Working with Marshall to archive his work allowed her to listen to Marshall's many stories and delve into his memories. Davis told CNN that what made Marshall's shots unique was that he always demanded total access to the rock stars.

"He really was everywhere with the musicians on the tour bus or offstage," Davis said. "He always had his camera with him. People ignored the camera in a sense. It was an extension of him. He had the ability to be a fly on the wall."

Marshall's ability to camouflage without disturbing the band's dynamic also allowed him to experience the touring life of the Rolling Stones, Davis said.

"It really set the precedent for the rock star concert tour," she said. "They had their own plane, lots of drugs, lots of alcohol. It was just crazy. There was a lot going on."

Davis said that Marshall's strong personality, fierce passion for music and his drive to get the best pictures while maintaining a sense of camaraderie made him relatable to musicians such as Richards.

"He was their friend," she said. "He partied with them. He had their trust. As Keith said in the foreword of the book, on the tour he was like another Rolling Stone."

But Marshall most enjoyed capturing those quiet moments, when the musicians took off their performer masks and were just themselves, she said. One only has to look at photos of Jagger onstage and off it to see the different personas.

"Mick was very business-oriented," Davis said. "Mick was much more serious than Keith. That's what a lot of people don't realize is that he was the businessman of the band."

Davis said that while Marshall spent a short time following the Stones, it was enough to create a bond with some of the members, especially Richards.

But the most important task for Marshall during his career, whether it was the Beatles' final concert in 1966 or Jimi Hendrix's performance during the Monterey Pop Festival in 1967, was to capture the feeling of music, a task that could seem quite impossible.

"Jim was always trying to show the true face of whatever he photographed," Davis said. "He shattered stereotypes of what rock stars are supposed to look like. He said, 'I was a historian with a camera and I didn't know it.' He was photographing pieces of history."